举一个非常简单的例子:
import pandas as pd
import numpy as np
import datetime
base = datetime.datetime(2016, 10, 1)
date_list = [base - datetime.timedelta(days=x) for x in range(0, 100)]
df1 = pd.DataFrame(np.random.randint(0,100,size=(100, 4)), columns=list('ABCD'), index = date_list)
df2 = pd.DataFrame(np.random.randint(0,100,size=(100, 4)), columns=list('ABCD'), index = date_list)
pd.merge(df1, df2, how = 'outer', left_on = True)
返回错误，TypeError:“NoneType”类型的对象没有 len()。如果我想在索引上合并这两个 DataFrame(相同的 DatetimeIndex)，我是否缺少合并的工作原理？
我正在运行 Python 2.7.12、Pandas 0.18.1 和 Numpy 1.11.1
完整的回溯是:
TypeError Traceback (most recent call last)
<ipython-input-1-3174c0ff542d> in <module>()
9 df2 = pd.DataFrame(np.random.randint(0,100,size=(100, 4)), columns=list('ABCD'), index = date_list)
10
---> 11 pd.merge(df1, df2, how = 'outer', left_on = True)
/Users/user/anaconda/lib/python2.7/site-packages/pandas/tools/merge.pyc in merge(left, right, how, on, left_on, right_on, left_index, right_index, sort, suffixes, copy, indicator)
36 right_on=right_on, left_index=left_index,
37 right_index=right_index, sort=sort, suffixes=suffixes,
---> 38 copy=copy, indicator=indicator)
39 return op.get_result()
40 if __debug__:
/Users/user/anaconda/lib/python2.7/site-packages/pandas/tools/merge.pyc in __init__(self, left, right, how, on, left_on, right_on, axis, left_index, right_index, sort, suffixes, copy, indicator)
208 (self.left_join_keys,
209 self.right_join_keys,
--> 210 self.join_names) = self._get_merge_keys()
211
212 def get_result(self):
/Users/user/anaconda/lib/python2.7/site-packages/pandas/tools/merge.pyc in _get_merge_keys(self)
405 left_keys, right_keys
406 """
--> 407 self._validate_specification()
408
409 left_keys = []
/Users/user/anaconda/lib/python2.7/site-packages/pandas/tools/merge.pyc in _validate_specification(self)
521 'of levels in the index of "left"')
522 self.left_on = [None] * n
--> 523 if len(self.right_on) != len(self.left_on):
524 raise ValueError("len(right_on) must equal len(left_on)")
525
TypeError: object of type 'NoneType' has no len()
最佳答案
在 documentation它指出:“left_on”可以是“标签或列表，或类似数组”当您传递“True”时，会出现错误。
如果你只是省略“left_on”，它似乎工作得很好。
我是否误解了这个问题？
也许你确实想这样做:
pd.merge(df1, df2, how = 'outer', left_index = True, right_index=True)
这会导致
A_x B_x C_x D_x A_y B_y C_y D_y
2016-10-01 99 9 89 27 2 10 63 44
2016-09-30 42 74 58 87 33 56 83 72
2016-09-29 89 41 89 94 75 66 74 17
2016-09-28 53 42 4 83 84 48 2 36
2016-09-27 81 97 1 14 86 27 49 53
关于python - Pandas 在 DatetimeIndex TypeError : object of type 'NoneType' has no len() 上合并，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40551492/